Variable color luminous device



Feb. 19, 1935. a P. L. SPENCER 1,991,775

' VAgIABLE COLOR Lvumous DEVI-CE Fil'ed Jan. 8, 1932 s Sheets-Sheet 1 lwmtq y: i

Afro/War Feb. 19, 1935. P. 1.. SPENCER 1,991,775

VARIABLE COLOR LUMIN QUS DEVICE Filed Jan. 8. 1932 5 Sheets-Sheet 2 Afro/v) PERCY L. SPENCER Patented Feb. 19, 1935 UNITED STATES PATENT OFFICE 1,991,715 I vanmnus COLOR LUMINOUS DEVICE of Delaware Application January 8, .1932, Serial No. 585,444 1': Claims. (c1. z4o 3.1

The present invention relates to a crm'lpos'itev source of light in which means are provided for varying the color of the light produced by said source.

An object of my invention is to produce such color variation while maintaining the brilliancy and. amount of the illumination constant.

Another object of my invention is the provision of means for varying the color in such a device in a predetermined manner.

A still further object of my invention is to provide means whereby aparticular color may be reproduced exactly whenever desired.

The foregoing and other objects of my invention will be best understood from the following-description of exemplifications thereof, references being had to the accompanying drawings, wherein Fig. l is a diagrammatic representation of one embodiment of my invention; I

Fig. 2 shows the developed surface of the switching device used in Fig. 1;

Fig. 3 illustrates the manner in which my comsubstantially 5 posite light may be mounted in front of a reflector;

Fig. 4 illustrates a modification of the control means associated with the switching device; Fig. 5 is a diagrammatic representation ofaniother embodiment of my invention;

Fig. 6 shows a still further embodiment of my invention; and

Fig. 7 consists of a set of diagrams illustrating the operation of the device, as shown in Fig. 5.

advertising, commercial processes, and the like,

manner. For example, in the display of various colored articles, such as gems, silks, etc., an illuminating source of varying color produces a particularly pleasing effect. Various schemes for varying the color of a source of light are known 'but have been found to be defective in that the variation in the color is accompanied by .a corresponding variation in the amount and intensity or brilliancy'of the illumination provided. Furthermore, such systems are difficult to control, and when a definite predetermined color was desired, it is difficult to secure that particular color. Such systems also lack flexibility of control. In accordance with my invention I provide a source of illumination which obviates the above disad- F vantages and also-presents certain other new and additional advantages. 3

" In various illuminating applications, such as.

- In Fig. 1 I have shown two gaseous discharge tubes 1 and 2. These tubes are each filled with a different gaseous or vaporous atmosphere, which when excited by an electrical discharge therein emit different definite characteristic light radiations. Although these tubes may be any type of luminous gas discharge tube, they preferably are constituted by an elongated sealed envelope formed in any desiredshape, carrying electrodes 3 and 4 in the ,opposite ends thereof between which the discharges are adapted to take place. I preferably fllltube 1 with a gas which emits a color which is predominantly red which gas may be, for example, neon, while tube 2 ispreferably filled with a gas emitting a complementary blue color, which gas may be, for example, mercury vapor. The two tubes 1 and 2 are placed together in such. a manner that the light emitted by said tubes is combined, and this combined light is used as a singl source of light. Tube 1 is preferably energized through a transformer 5, and tube 2 through'a transformer 6.

The two electrodes 3 are connected together by a conductor '7, and the conductor 7 is connected by means of the conductor 9 to one terminal of the secondary 8 of the transformer 5. The other terminal of secondary 8 is connected by means of the conductor 10 to the electrode 4 of tube 1.

The secondary 11 of transformer 6 has one ter-'- minal thereof connected-by meansof a conductor 12 to the conductor 9, while the other terminal of the secondary 11 is connected by means of the conductor 13 to the electrode 4 of tube 2. Thus it will be seen that the two electrodes 3 and 4 of tube 1 are connectedacross the secondary 8 while the electrodes Band 4-of tube 2 are connected across the secondary 11. The primaries l4 and 15 of the transformers 5 and 6 are energized from a source of alternating current which maybe, ior example, the two wires 17 and 18 of an alternating current line. One terminal of each of'the primaries 14 and 15 of the transformers 5 and 6, respectively, is connected together by means. of a conductor 19. This common conductor is connected by means of another conductor 20 to the line 18. The opposite ends of the secondaries 1-4 and 15 are connected respectively to brushes 21 and 22 by means of conductors 23 and 24, respectively. These brushes 21 and 22 bear upon the end portions of the drum 25 of a switching d'evice16. An adjustable brush 26 bears upon the drum 25 at some portion intermediate the brushes 21 and 22, and

is connected by meansof a conductor 27 to the other alternating current line 17. The switching drum 25- consists essentially of two interfltting conducting portions 28 and 29, insulated from each other. of a series of wedge-shaped commutator bars 30 connected at the outer end of the drum by a slipring portion 31, while the conducting portion 29 consists of a series of wedge-shaped commutator bars 32 connected at the other end of the drumv by a slip-ring 'portion' 33. The sections 28 and 5 29 are insulated from each other by a zig-zag strip of insulation 34. It will be noted that the brush 21 bears upon the slip-ringportion 31 while the brush 22 bears upon the slip-ring portion 33. Brush 26 rides alternately. omcommutator bars 30 and 32. The drum 25 may be rotated by any convenient means, which preferably consists of a motor 35 which also may be energized from the alternating current lines 1'? and 18. This motor 35 drives the drum 25 through a gear reduction system 36, whereby the speed of the drum 25 may be any desired speed. It will be understood that the gear reduction system 36 may be variable in order that the speed of the drum may be varied. In the arrangement as shown in Fig. 1, the brush a 26 is reciprocated in a direction parallel with the A scale 41 may be provided to indicate the speed at which the brush 26 is reciprocated so that by setting the'control element 40 in a certain predetermined position on the scale 41, the brush 26 is reciprocated at a certain predetermined rate.

The operation of the device shown in Figs. 1

and 2 is substantially as follows. When the alternating current lines 17 and 18 are energized,

, themotor 35 is set in operation, rotates the drum brush 26 comes into contact with the wedge- 25, and reciprocates the brush 26. When the brush 26 rides along the slip-ring portion 33, transformr 6 and consequently tube 2 are energized by the following circuit: line 17, conductor 27, brush 26, slip-ring section 33, brush 22, conductor 24, primary 15, conductor 19, conductor 20, and line 18. The connection through the primary 14 of the transformer 5, however, is broken by the insulating strip 34. Thus the tube 2 which emits the blue radiation is energized while "the tube 1 remains unenergized. The light which then will be emitted by my composite illuminated device will be the blue radiation emitted by the tube 2. ,As the brush 26 moves over onto the wedge-shaped commutator bars, the tube 2' will remain energized through the same circuit as long as the brush 26 is on the wedge-shaped bars 32, while the tube 1 becomes energized when the shaped commutator bars 30. The energizing circuit for tube 1 less follows: line 17, conductor 27, brush 26, commutator bar 30, slip-ring 31, brush 21, conductor 23, primary 14, conductors 19 and 26, and line 18. The tubes 1 and 2 are thus energized alternately until the brush 26 rides on the slip-ring portion 31, when the tube 1 alone is energized and the light emitted by-the device is thered radiation of tube 1.

It will be noted that as the brush 26 leaves one of the commutator bars andcontacts with the adjacent commutating bar, the entire voltage of either the secondary '8 or the secondary 11 is impressed directly across the tubes 1 and The conducting portion 28 consists- 2, respectively. Thus the respective tube is illuminated to full brilliancy as the brush 26 comes in contact with the commutator bar. However, the relative periods during which' the tubes 1 and 2 are illuminated will depend upon the position of the brush 26 with respect to the switching drum 25. The closer the brush 26 is to the slip-ring section 33, the greater will be the period of time during which the tube 2 is illuminated, and correspondingly smaller will be the period of time during which the tube 1 is energized. As the brush 26, however, travels toward the slip-ring section 31, the length of time during which the tube 2 is energized decreases; while the length of time that the tube 1 is energized increases. each of the tubes 1 and 2 varies in alike manner with the relative length of time during which each one of said tubes is energized. Since only one tube is energized during any given instant, and as soon as that tube is de-energized, the other tube is energized, the total effect is that of a single tube energized continuously. Thus it will be seen that the intensity or brilliancy and total amount of light emitted by my device will remain constant no matter in what position the brush 26 is placed. It is merely the relative lengths of the periods of energization of the two tubes that vary, which variation, however, causes a corresponding variation in the composite color furnished by my illuminating device. It is known that the combination of a red and blue light will produce various colors lying between these two colors. The resultant color will depend only upon the relative amounts of the blue and red light. The greater the proportion of red light there is, the closer will the resultantlight be to red, while the greater the proportion of blue light there is, the closer will the resultant light be to green. Thus the color variation proceeds from the blue of the tube 2 through all possible combinations with the red of tube 1 to the pure red of tube 1, as the brush 26 travels from the slipring 33 to the slip-ring 31. When the brush 26 travels back toward the slip-ring section 33, the color varies in the inverse direction.

In order to eliminate flicker effects, the drum 25 is rotated at such a speed that the frequency with which the tubes 1 and 2 are energized is in excess of that which the human eye, due to the persistence of vision, can distinguish. Such a rate-is preferably about twenty energizations per second. Since the adjustable gear reduction system 39 controls-merely the double-thread screw 3'7, the speed at which the brush 26 travels back and'forth along thedrum 35 and consequently the rapidity with which the variation in color Thus the amount of light generated in occurs, .can take place independently of the frequency of the energization impulses supplied to the tubes l and 2.

The tubes 1 and 2 may be mounted in any convenient manner, Fig. 3 showing one example of such mounting. In Fig. 3, 42 is a curved reilec- The tubes 1 and 2 areplaced with device varies continuously in a predetermined manner, it is often desirable to provide such a source of'illumination of 'a predetermined constant color. .Such a source of light has been found to be very useful in ,various' commercial processes, such as, for example, where it is desirable to classify materials'according to their color. In Fig. 4 I have shown an arrangement whereby my illuminating device may be set for any definitecolor, and any such color may be provided whereby itmay -be set at any definite cator 47 may be calibrated in terms ofcolor or in accordance with any other desired system'of marking. As pointed out above. the resultant color emitted by my tubes 1 and 2 depends upon ,the relative lengths of time during which each of these tubes is energized. By setting the brush 26 at some definite position on the drum 25, these relative lengths of time remain invariable, and thus the composite color emitted remains I invariable. By shifting the brush 2s alongthe drum 25, the relative lengths of the periods change. However, when the brush 26 is placed in its new position, the new relative periods during which the tubes 1 and 2 are'energized also remain invariable. In each case the total amount of light emitted by. the composite illuminating device remains constant. The rate of rotation of the drum 25 in Fig. 4 is similar .to that specified for Fig. 1, whereby the frequency at which the tubes 1 and 2 are energized is such that theirequency of the light flashes is too great for the human eye to follow.

Instead of supplying curr'ent impulses to each of the tubes 1 and 2 by mechanical switching means, I may employ purely electrical switching means. 'In such electrical switching means, use may be made of grid-controlled thermionic gas discharge tubes commonly known as thyratrons. Oneof such systems employing electrical switbhing means is. shown in Fig.5. The system, as shown in Fig. 5, employs two gaseous discharge tubes 1 and 2, as in Fig. 1, emitting respectively characteristic red and blue light when energized.

Each of the tubes 1 and 2 is energized from the alternating current lines 47,and 48 throughtransformers 49'and 50, respectively. The alter nating current linesmay be supplied with the usual -cycle, 110 or 220-volt alternating cur--v rent, although it is obvious that any other voltage Ithe opposite ends of secondary56 and transformer 50. The primaries 57 and 58 of transformers 49 and 50 are each connected across alternating current lines 4'! and .48 in series with the grid-controlled gas discharge tubes 59 and 60, respectively. One end of the primary 57 is connected directly to the anode 61 of tube 59, the other end of said primary being connected by means of a conductor 82'to the alternating current line 47. The cathode 63 of the tube 59 is connected by means of conductors 63 and 64 to the other alternating current line 48. In a similar manner one end of primary 58 of transformer 50 is connected directly to the anode 65 of tube 60, the other end of said primary 58 being con-v nected by means of a conductor 66 to the alternating current line 48. The cathode 67 of tube 60 is connected by means of conductors 68 and 69 to the other alternating current line 47. The cathodes 63 and 67 of tubes 59 and 60, respectively, are thermionic cathodes, which when heated to their operating temperatures, emit large nur n,

the drawinga by way of example, as filamentary cathodes which are energized respectively from the heating transformers 70 and 71. In order f bers of electrons. These cathodes are shown in to control the discharge between the cathode and anode of each of the tubes 59. and 60, these tubes are provided respectively with control grids 72 and 73. The control grid'72 is connected to the cathode 63 through the secondary winding 74 of a transformer '75, while the control grid 73 is connected to the cathode 67 of tube 60 through the secondary 76 of the transformer 77. The primaries 78 and 79 of-the transformers and 77, respectively, are each connected across the alternating current lines 47 and 48. Interposed in these connections are phase-shifting devices 80 and 81 for the primaries 78 and 79,. respectively. These phase-shifting devices may be of any desired'type, but preferably are those which can shift the phase of the output side, of said phase-shifting device through an angle of .The two phase-shifting devices 80 and 81 are gl'zed, it becomes heated and emits electrons.-

When a voltage is impressed across the cathode and anode in such a direction that the anode is positive, electrons emitted from the cathode will be attracted toward the anode, and during its travel will ionize the gas or vapor within the tube, whereby large numbers'of ions or current carriers are created. The existence of these large numbers of current carriers results in comparatively large currents passing through the tubewith very low voltage drop. However, if before a discharge is started through the tube, a negative. potential is impressed upon the control grid, the'electrons emitted from the cathode will be repelled back toward the cathode before they havea chance toproduce any appreciable ionization, and therefore as long as this negative potential exists on the control grid, the discharge will not occur. control'grid is less'than a certain proportion of the total voltage across the cathode and anode, or if the potential on the grid becomes zero or positive, thedischargewill start. Once the discharge is started'fithe number, of current carriers created is so large that any subsequent variation in potential on the control grid exerts practically no control on the discharge. As soon, however,

If the negative potential on the anode 61.

as the potential across the cathode and anode reverses, the current will cease to flow inasmuch as the anode does not emit electrons, and any electrons emitted from the cathode are immediately attracted back into the cathode. In the system as shown in Fig. 5, I preferably choose the constants of my tubes and the voltages used such that as long as the grids 72 and 73 are appreciably negative, the discharge will not be able to start in the respective tubes 59 and 60. However, as soon as the. potential on thegrids 72 and 73 becomes positive, a discharge will start provided the voltage between the cathode and anode of the respective tubes is in the proper direction, that is, the anode is positive. Although, practically, a discharge will not start until the anode voltage is appreciably positive and the discharge will not be shut off unless the grid is appreciably negative, I will analyze the operation of my system, assuming that the discharge starts assoon as the anode is positive, with a zero or positive grid, and also that as long as the grid is negative at all, no discharge will start. Since these conditions can be closely approximated in a practical system, the following analysis will represent the actual operation except for a slight shift in the time at which the discharges start and stop.

The operation of my device will be evident by referring to Fig. '1 in conjunction with Fig. 5. The curve n represents the voltages in the tube 59 which control the discharge through the red tube 1. Curve 0 represents the voltage conditions in the tube 60 which control the discharge through the blue tube 2. In the curves a and y, the heavy sine waves represent the voltageson the anodes 61and 65, respectively. The other sine waves represent different voltages on the grids leading the voltages on the anodes by the number of degrees indicated. Curves b, c, d, e and f represent the periods of energization of the red and blue tubes 1 and2, respectively, during one complete current cycle. The full lines represent the periods. of energization of the red tube 1 while the dotted lines, the periods of energization of the blue tube 2. With the regulating device 82 in one of its extreme positions, the voltage on the grid 73 will be 180 out of phase with the voltage on anode 65, while the voltage on the grid 72 will be in phase with the voltage on It will be noted that the two tubes 59 and 60 are connected so that voltage supplied to them is ordinarily 180 out of phase. The voltages in tube 59 under the above conditions are represented by the sine wave labelled 0 in curve 0. Since the anode and grid voltages are in phase, the grid '12 will be positive at the same time as the anode 61 is positive. Thus the discharge through tube 59 will start as soon as the anode 61 becomes positive, and will continue throughout an entire half cycle of the alternating current. Thus the tube 1 will be energized through this complete half cycle, as indicated by the block labelled red" on the curve b. In the above-mentioned position of adjustment of the control device 82, the voltage on the grid 73 will be that represented by the sine wave labelled 180 in curve 9. It will be noted that as long as the anode 65 is positive, the grid 73 will be negative so that a discharge cannot start through the tube 60, and therefore the tube 2 will remainv unenergized throughout the entire current cycle. Thus theilluminating conditions are represented by the curve b, which shows that only the red l sht of the tube 1 is being emitted. As the control device 82 is moved out of its entrtme position, the phase-shifting devices and 81 are so arranged that the voltage on the grid 72 advances in phase and leads the anode voltage 61, while the voltage on the grid 73 drops backin phase and gradually approaches the voltage of anode 65. At some intermediate position the voltage on the grid 72 will lead the anode voltage by 45, and at the same time the voltage on the grid 73 will lead the voltageof anode 65 by 135. Under these conditions, the sine wave 45' in curve 0 represents the grid voltage '12, while the sine wave 135 of curve 0 represents the voltage of grid 73. Thus it will be seen that as the anode 61 becomes positive, the grid 72 still is negative, and does not become positive until 45 later. At this point, 'however, the grid '72 does become positive, and the discharge is initiated through the tube .59 and consequently throughthe tube 1. The grid '73, however, remains negative and does not become positive until the anode 65 has been positive for 135 of the positive current cycle. As soon, however, as the grid '13 does become positive, a discharge will pass through the tube 60 and the tube 2 will be energized. The periods of energization under these conditions are represented by the curve 0, the block labelled "red" indicating the energization period of the tube 1, and the block labelled blue representing the period of energization of the tube ,2. 1 By a similar analysis it will be seen that as the voltage in the grids 72 and '73 lead-their anode voltages respectively by the period of energization of the tubes 1 and 2 will be thatrepresented by curve d, while when the grid voltages lead their anode voltages by and 45, respectively, curve e represents the energization conditions. When finally the voltage of grid '72 is out of phase with its anode voltage and the voltage of grid '13 is in phase with its anode voltage, the energization of tubes 1 and 2 is represented by curve 9.

From the above analysis it will be noted that the intensity of illumination at any given instant of the system shown in Fig. 51s that of a single tube, while the total amount of illumination during any single current cycle remains constant. This condition is very similar to that. of the device as shown in Fig. 1. Thus the adjustment of the regulating device 82 results merely in a change of the relative lengths of time during which the tubes 1' and 2 are energized without producing any variation in either the intensity or the amount of light emanating from my illuminating device. The variation in the relative periods of energization of the two tubes produces a variation in color exactly as described for Fig. 1.

' Instead of using alternating current on the grids of the controltubes, a direct current .bias may be em loyed. By properly choosing the magnitude of the negative bias on the grid, the discharge can be caused to start at any desired point during the first half of the positive part of the anode voltage swing. By varying this bias, the point on the current cycle at which the tube becomes conducting is varied, and therefore, a variation in the length of the period din'ing which the respective illuminating tube is energized is likewise varied. Such an arrangement is shown in Fig. 6. In this figure the arrangement is identical with that shown in Fig. 5, except for the manner in which the voltage is applied to and varied on the control grids 72'and 73. In Fig. 6

a potentialis impressed upon the grids 72 and '73 by means of potentiometers 84 and 85. These potentiometers each consists of resistances 86 and 87 across batteries 88 and 89, respectively.

. of a conductor 93 while the conductor 94 connects grid 73 to the adjustable contact 90. The positive ends of the potentiometers 84 and 85 are connected respectively to the cathodes 63 and 64 of the tubes 59 and 60 by means of conductors 95 and 96 leading to the respective cathode leads64 and 69. The control device 92 may also be provided with an indicating scale 97 which may be calibrated as is scale 83 of Fig. 5. It will be noted that as in Fig. 5, the voltages applied to the tubes 59 and 60 are 180 out of phase. The potentiometers 83 and 84 are so adjusted that in one extreme position of the regulating device 92, zero potential is impressed on the grid 72, while full negative potential is impressed upon the grid 73. In this condition a disdischarge starts through the tube 59 as soon as the anode 61 becomes positive, and the tube 1 is energized throughout each positive half cycle of the alternating current source. The negative potential, however, on the grid 73 effectively blocks thestarting of any discharge through the tube 60, and therefore the tube 2 remains extinguished. This condition may be that as represented by curve I) of Fig. 7. As the regulating device 92 is'moved out of its extreme position, the grid 73.

becomes less negative while the grid 72 acquires a small negative bias. The smaller bias on the grid '72 is insufficient to stop the dischargewhen the alternating voltage on the anode 61 reaches'its peak value. Thus a discharge will start and the tube 1 will be energized through part of the positive half. cycle of the alternating current source. The negative bias on the grid 73 will be suflicient to prevent the start of the discharge for a small period of time after the anode 51 becomes positive. Thus it will be seen that the period of energization of the tube 1 is shortened while the period of energization of the tube 2 is increased. As the regulating device 92 is moved farther and farther toward its other extreme position, the

period of energization of the tube 1 becomes increasingly lengthened, while that of the tube 2 becomes shortened until finally only the tube 2 is energized while the tube-1 is entirely extinguished. The net result of the arrangement, as shown in Fig. 6, is likewise a source of illumination which remains constant in intensity and amount of light emitted, but in which the current is varied in accordance with the adjustment of the control 92.

This invention is not limited to. the particular details of construction, materials andprocesses described above as many'equivalents will suggest themselves to those skilled in the art. For example, instead of using two tubes as specified, any number of tubes emitting difierent colors may be utilized. The colors of these tubes would, of

course, be complementary colors, and may con-- sist of more than merely the two colors, blue and red. For instance, use could be made of the combination of a blue, red and yellow tube.

What is claimed-is: r

1. The method of controlling aplurality of juxtaposed light sources emitting light radiations lying in different portions of the light spectrum, which consists in energizing all of said sources at a constant intensity and in such a amount of light emitted by said sources simultaneously in opposite directions, keeping the total amount of light emitted by said combined light sources constant in any given period of time, whereby the intensity and amount of light emitted by said combined light sources in any given period oftime remains substantially constant for said period.

2. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions of the light spectrum,

-means for intermittently and successively ener-.

gizing said sources at a frequency greater than that distinguishable by the human eye, and means for varying the relative lengths of the periods of energization of said sources.

3. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions of the light spectrum, means for intermittently and successively energizing said sources at a frequency greater than that distinguishable by the human eye, and means for continuously varying the relative lengths of the periods of energization of each of said sources.

4. An illuminating device comprising a, plurality of light sources emitting light radiations lying in difierent portions of the light spectrum, means for intermittently and successively energizing said sources at a frequency greater than that distinguishable by the human eye, andmeans for varying the relative lengths of the periods of energiza-' tion of said sources, said means being so ad- .justable that the lengths of the periods of energization of said sources may be predeterminately set at,any desired constant ratio.

5. An illuminating device comprising a plurality of light sources emitting light radiations lying in diilerent portions of the light spectrum, and means for intermittently and successively energizing said sources at a frequency greater than that distinguishable by the human eye in such a way that the energization of each source is out of phase with the energization of the succeeding source.

6. An illuminating device comprising a plurality of, light sources emitting light radiations lying in different portions of the light spectrum, a commutating device for intermittently and successively energizing said light sources in such a way that the energization of each source' is out of phase with the energization of the succeed- ;ing source, said commutating device being opdifferent portions of the light spectrum, means for intermittently energizing said light sources, said means comprising a controlled gaseous discharge tube connected to each of said light sources, each of said tubes comprising a gas-filled envelope containing a cathode and an anode, means for supplying an alternating voltage across the cathode and anode of each of said tubes, and means for controlling the discharge between said cathode and anode, whereby the conductivity of each of said tubes and the energization of each. of said light sources may be controlled.

8. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions of the light spectrum", energizing means-connected to said light sources for energizing said light sources and for energiz-' ing' and-controlling each of said light sources, said 9. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions of the light spectrum, a source of current for energizing each of said sources, a

common switching device interposed between said current source and said light sources, said switching device comprising a rotatable drum carrying interiitting wedge-shaped commutator bars, each alternating commutator bar being insulated from its adjacent commutator bar, said bars being connected in sets, each of said sets being connected to one of said light sources, a brush for energizing each of said commutator sets, said brush being adjustable along said drum, whereby the relative lengths of the periods of energization of said light sources may be varied.

10. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions of the light spectrum, a source of current for energizing each of said sources, a common switching device interposed between said current source and said light sources, said switching devicecomprising a rotatable drum carrying interfitting wedge-shaped commutator bars, each alternating commutator bar being insulated from its adjacent commutator bar, said bars being connected in sets, each of said sets being connected to one of said light sources, a brush for energizing each of said commutator sets, said brush being adjustable along said drum, whereby the relative lengths of the periods of energization of said light sources may be varied, and means for continuously reciprocating said brush.

said brush being adjustable along said drum,

wherebythe relative lengths of the periods of energization or said light sources may be varied, means for continuously reciprocating said brush, and means for regulating the speed or reciprocation of said brush.

12. An illuminating device comprising a plurality or light sources emitting light radiations lying in diil'erent portions of the light spectrum,

means for intermittently and successively energizing said light sources, said means comprising a grid-controlled gaseous discharge tube connected to each of said light sources, each of said tubes consisting of an evacuated gas-filled container enclosing a thermionic cathode and anode and a control grid, means for supplying an alternating'voltage across the cathode and anode of each 0! said tubes. means for supplying a voltage ternately to said grid, and means for controlling said grid voltage, whereby'the conductivity of each of said tubes and the energization of each 01' said light sources may be controlled.

13. An illuminating device comprising a plurailty or light sources emitting light radiations lying in different portions of the light spectrum, means for intermittently and successively energizing said light sources, said means comprising a grid-controlled gaseous discharge tube connected toeach or said light sources, each of said tubes consisting oi! an evacuated gas-filled container enclosing a thermionic cathode, anode, and a control grid, means for supplying an alternating voltage across the cathode and anode of each of said tubes, means for supplying an alternating voltage to each of said grids, means for shifting the phase or the voltage supplied to said grids with respect to the voltage across its associated cathode and anode, whereby the conductivity oi each of said tubes and the energization of each of said light sources may be controlled.

14. An illuminating device comprising two light sources emitting light radiations lying in diiierent portions of the light spectrum, means for alenergizing said light sources, said means comprising a grid-controlled gaseous discharge tube connected to each of said light sources, each of said tubes consisting 01 an evacuated gas-filled container enclosing a thermionic cathode, anode, and a control grid, means for supplying an alternating voltage across the cathode and anode of each oi said tubes, said voltages being 180 degrees out oi phase, means for supplying an alternating voltage to said grid, means for shifting the phase of each oi said grid voltages with respect to the voltage across its corresponding cathode and anode in such a manner that when the voltage on one of said grids is in phase with its corresponding cathodeanode voltage, the voltage on the other 0! said grids is 180 degrees out of the phase with respect to its cathode-anode voltage, said phaseshifting means being adapted to shift the phase oi. the voltages of said grids in opposite directions.

15. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions 0! the light spectrum, means for intermittently and successively energizing said light sources, said means comprising a grid-controlled gaseous thermionic discharge tube connected toeach of said light sources, each of said tubes consisting oi an evacuated gas-filled container enclosing a thermionic cathode, anode, and a control grid, means for supplying an alternating voltage across the cathode and anode of each of said tubes, means for supplying a negative bias to each of said grids, and means for controlling the magnitude of said negative bias, whereby the discharge across each of said tubes and the energization of each 0! said light sources may be controlled.

16. An illuminating device comprising a pinrality of light sources emitting light radiations lying in different portions or the light spectrum, means for intermittently energizing said sources at a frequency greater than that distinguishable by the human eye, and means for varying relative lengths of the periods or energization of said sources.

17. An illuminating device comprising a plurality of light sources emitting light radiations lying in different portions or the light spectrum, means for intermittently energizing said light 1,991,775 r 7 sources, said means comprising a grid-controlled for supplying a voltage to said control electrode,

gaseous discharge tube connected to each of said and means for controlling said control electrode gas-filled container enclosing a thermionic cathlight sources, each of said tubes consisting of a voltage, whereby the conductivity of each of said tubes and the energization of each of said light ode, an anode, and a control electrode, means sources may be controlled.

- for supplying an alternating voltage across the cathode and anode of each of said tubes, means PERCY L. SPENCER. 

